Krdytkyu

I think htop is the best solution.

• sudo apt-get install htop

This way you will notice what programs is using most RAM. and you can easily terminate one if you want to. Here's a screenshot!

If you looking for a nice breakdown of the memory used by each running process, then I might recommend checking out ps_mem.py (found here at pixelbeat.org).

I know in the comments above, you mentioned wanting a one-line snapshot from free, but I figured others might find this useful.

Example output:

user@system:~$ sudo ps_mem.py

[sudo] password for user:

 Private  +   Shared  =  RAM used       Program



  4.0 KiB +   7.5 KiB =  11.5 KiB       logger

  4.0 KiB +   8.0 KiB =  12.0 KiB       mysqld_safe

  4.0 KiB +  10.0 KiB =  14.0 KiB       getty

  4.0 KiB +  42.0 KiB =  46.0 KiB       saslauthd (5)

 48.0 KiB +  13.0 KiB =  61.0 KiB       init

 56.0 KiB +  27.5 KiB =  83.5 KiB       memcached

 84.0 KiB +  26.5 KiB = 110.5 KiB       cron

120.0 KiB +  50.0 KiB = 170.0 KiB       master

204.0 KiB + 107.5 KiB = 311.5 KiB       qmgr

396.0 KiB +  94.0 KiB = 490.0 KiB       tlsmgr

460.0 KiB +  65.0 KiB = 525.0 KiB       rsyslogd

384.0 KiB + 171.0 KiB = 555.0 KiB       sudo

476.0 KiB +  83.0 KiB = 559.0 KiB       monit

568.0 KiB +  60.0 KiB = 628.0 KiB       freshclam

552.0 KiB + 259.5 KiB = 811.5 KiB       pickup

  1.1 MiB +  80.0 KiB =   1.2 MiB       bash

  1.4 MiB + 308.5 KiB =   1.7 MiB       fail2ban-server

888.0 KiB +   1.0 MiB =   1.9 MiB       sshd (3)

  1.9 MiB +  32.5 KiB =   1.9 MiB       munin-node

 13.1 MiB +  86.0 KiB =  13.2 MiB       mysqld

147.4 MiB +  36.5 MiB = 183.9 MiB       apache2 (7)

---------------------------------

                        208.1 MiB

=================================



 Private  +   Shared  =  RAM used       Program

The only part I don't like is the fact that the script claims to require root privileges. I haven't had an opportunity yet to see exactly why this is the case.

Use the free command.
For example, this is the ouput of free -m:

             total       used       free     shared    buffers     cached

Mem:          2012       1666        345          0        101        616

-/+ buffers/cache:        947       1064

Swap:         7624          0       7624

free -m | grep /+ will return only the second line:

-/+ buffers/cache:        947       1064

The watch command may be useful. Try watch -n 5 free to monitor memory usage with updates every five seconds.

You can do it using cat /proc/meminfo.

MemTotal:        4039160 kB

MemFree:          309796 kB

MemAvailable:    3001052 kB

Buffers:          345636 kB

Cached:          2341288 kB

SwapCached:            8 kB

Active:          1725160 kB

Inactive:        1551652 kB

Active(anon):     538404 kB

Inactive(anon):    70076 kB

Active(file):    1186756 kB

Inactive(file):  1481576 kB

Unevictable:          32 kB

Mlocked:              32 kB

SwapTotal:       4194300 kB

SwapFree:        4194044 kB

Dirty:                 0 kB

Writeback:             0 kB

AnonPages:        589988 kB

Mapped:           255972 kB

Shmem:             18596 kB

Slab:             374888 kB

SReclaimable:     310496 kB

SUnreclaim:        64392 kB

KernelStack:        6976 kB

PageTables:        26452 kB

NFS_Unstable:          0 kB

Bounce:                0 kB

WritebackTmp:          0 kB

CommitLimit:     6213880 kB

Committed_AS:    3589736 kB

VmallocTotal:   34359738367 kB

VmallocUsed:           0 kB

VmallocChunk:          0 kB

HardwareCorrupted:     0 kB

AnonHugePages:         0 kB

ShmemHugePages:        0 kB

ShmemPmdMapped:        0 kB

CmaTotal:              0 kB

CmaFree:               0 kB

HugePages_Total:       0

HugePages_Free:        0

HugePages_Rsvd:        0

HugePages_Surp:        0

Hugepagesize:       2048 kB

DirectMap4k:      147392 kB

DirectMap2M:     4046848 kB

For visual monitoring of overall RAM usage, if you use Byobu, it will keep your memory usage in the lower right-hand corner of the terminal and will run while you are in any terminal session.

As you can see from screenshot, my virtual machine has a 1h3m uptime, 0.00 load, has 2.8GHz (virtual) processor and 994MB (21%) of the RAM available on the system.

Single line solution and output:

free -m | grep "Mem:"

Here is an example of the expected output:

Mem:           3944         652         302          18        2990        2930

I would use Cacti. This will graph your memory usage etc over a period of time, and you will be able to check on usage using your web browser.

Monitoring Memory Usage

I'm more in line with one of the preceding posts that mentioned Cacti as a great way to monitor memory usage. However, since it appears cacti is no longer popular in the mainstream, there is an alternative graphing application called Graphite.

Graphite is relatively easy to install on a ubuntu server and to install it, you can check out this link for the easy to follow installation procedures.

After graphite has been installed, now, you can send memory metrics to it, at whichever interval you wish; every 5 seconds, every minute, every hour...etc.

To graph memory metrics, as already suggested in previous posts, you can write your own script using system tools to gather the necessary memory information. Or, you can use a prewritten snmp plugin that'll do all the work for you.

If you wish to write your own memory script, it'll be wise to ensure you account for buffered and cached memory when calculating used memory, otherwise, you'll end up gathering false data.

If you wish to instead utilize an snmp plugin that already does all the necessary calculations for you, here's a link to one that works pretty well: checkMemoryviaSNMP.

Pros of SNMP:

I have snmp installed on all the remote nodes I monitor. This allows me to monitor all my systems from one central server(s), without having to copy or put a plugin on the remote nodes.

Cons of SNMP:

You'd have to ensure the snmp agent is installed on each of the remote nodes you wish to monitor memory on. However, this installation will be a one time deal. If you're using automation tools such as chef or puppet or similar tools in your environment, then this isn't a problem at all.

Configuration of the SNMP agent on the remote node(s):

After the snmp agent has been installed, simply vi the /etc/snmpd/snmpd.conf file and add this line to it:

rocommunity  (specify-a-community-string-aka-password-here)

Then restart the snmpd agent, with:

/etc/init.d/snmpd restart

Then, on your central server, from which you instead to monitor all your other servers, you can run the following command:

$ time ./checkMemoryviaSNMP -v2 public gearman001.phs.blah.com 30 90 graphite,10.10.10.10,2003,typical

WARNING: Used = [ 3.26154 GB ], Installed = [ 5.71509 GB ], PCT.Used = [ 57.069% ], Available.Memory = [ 2.00291 GB ]. Buffer = [ 137.594 MB ], Cached = [ 1.3849 GB ]. Thresholds: [ W=(30%) / C=(90%) ].  System Information = [ Linux gearman001.phs.blah.com 2.6.32-504.30.3.el6.x86_64 #1 SMP Thu Jul 9 15:20:47 EDT 2015 x86_64 ].



real    0m0.23s

user    0m0.03s

sys     0m0.02s